KATHMANDU, March 2: US Secretary of State John Kerry will meet his Russian counterpart later for talks in Geneva on the Ukraine crisis.
The talks come ahead of a new UN report documenting human rights violations by Ukrainian forces and pro-Russia rebels.
Mr Kerry is also expected to call for a transparent inquiry into the killing of a Russian opposition politician.
Boris Nemtsov is believed to have been working on a report detailing the presence of Russian troops in Ukraine before he was shot in Moscow on Friday.
His allies have accused the Kremlin of involvement, but Russian President Vladimir Putin condemned the murder as “vile” and vowed to find the killers.
The BBC’s Barbara Plett Usher in Geneva says Mr Kerry will be pressing Russian Foreign Minister Sergei Lavrov for an investigation into not only who pulled the trigger, but who ordered, funded and coordinated the murder.
Later John Kerry and Iran’s Foreign Minister Mohammad Javad Zarif will renew their negotiations on Tehran’s nuclear programme.
There is an end of March deadline to finally reach agreement on limiting the programme, in return for an easing of economic sanctions on Iran.
The talks on Ukraine are expected to be tense after Mr Kerry last week accused Russian officials of lying to him about Moscow’s support for rebels in eastern Ukraine.
The Ukrainian government, Western leaders and Nato say there is clear evidence that Russia is helping the rebels with heavy weapons and soldiers.
Independent experts echo that accusation but Moscow denies it, insisting that any Russians serving with the rebels are “volunteers”.
A fragile ceasefire continues to hold in Ukraine despite some violence in recent days.
On Saturday, Ukrainian photographer Sergiy Nikolayev was killed after being hit by a mortar shell in the village of Pisky near Donetsk.
Ukrainian military spokesman Andriy Lysenko said eight soldiers had been injured over the weekend by rebel shelling, while a separatist spokesman said Ukraine’s armed forces had also fired mortar rounds near Donetsk.
Both sides have begun pulling back some heavy weaponry from the front line – one of the conditions of the ceasefire agreement signed in the Belarusian capital Minsk last month.
Monitors from the OSCE security group have reported weapons movements on both sides but say it is too early to confirm a full withdrawal.
Speaking at the UN Security Council on Friday, OSCE envoy to Ukraine Heidi Tagliavini said the current situation was at a “crossroads” where the risk of further escalation remained high despite “encouraging signs”.
A US official travelling with Mr Kerry told reporters it was “too soon to tell” if the ceasefire would lead to an end in violence.
Fighting began in Ukraine’s eastern Donetsk and Luhansk regions last April, a month after Russia annexed the Crimea peninsula.
The UN has estimated that around 6,000 people have died since then, although it believes the real figure could be considerably higher.